This application claims the priority of German Application No. 103 01 531.0, filed Jan. 17, 2003, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device and a method for operating an electrical machine for a motor vehicle.
In motor vehicles, electrical machines are used as a generator for charging one or more vehicle power supply system batteries. The battery provides the electrical power which is required for starting the internal combustion engine for the propulsion system, for the vehicle external lighting, for the vehicle internal lighting and for other auxiliary units such as the air conditioning, seat heating, refrigerator or freezer compartment, windscreen wipers and similar electrical appliances. During normal charging operation, when the electrical machine is operated as a generator, it in each case produces the current which is drawn by the electrical loads from the battery. The electrical machine is driven by a control device, which is preferably formed by power electronics. The electrical machine is driven by preset voltages, voltage ramps and current limits. If the drive for the electrical machine is controlled such that the torque requirements for the propulsion system have priority, then there is a risk that the supply to the vehicle power supply system and the battery will be insufficient. If, on the other hand, the drive for the electrical machine is controlled by the vehicle power supply system management to have priority, taking account of the current demand of the vehicle power supply system and the respective state of charge of the battery at that time, then the advantages of the electrical machine for the propulsion system are utilized only inadequately.
The invention is intended to achieve the object of avoiding the drive for the electrical machine having disadvantageous influences on the propulsion system, in particular in the form of sudden torque changes, or on the vehicle power supply system and the vehicle battery, without this resulting in any restriction to the functionality of the propulsion system, or to the vehicle power supply system or the vehicle power supply system battery.
According to the invention, the solution comprises a device and a method for open-loop or closed-loop control of the electrical system and the propulsion system of a motor vehicle. The propulsion system has an internal combustion engine and a transmission with a variable step-up and/or step-down ratio. The electrical system has a vehicle power supply system and at least one battery connected to it. At least one electrical machine is provided which can be driven during normal charging operation as a generator for supplying current to the battery and to the vehicle power supply system from the propulsion system, in which case the electrical machine can also be driven by the propulsion system as a generator in a recuperation mode in order to produce a braking torque, and can likewise supply the battery and the vehicle power supply system with current in this case. The electrical machine can preferably also be operated as an electric motor in order to emit torque to the propulsion system. The device is designed to control the at least one electrical machine in different operating states by different signals, in which case a charging voltage for the normal charging mode is produced automatically as a voltage reference variable for controlling the electrical machine from signals from vehicle management as a function of the respective requirements for electrical power from the vehicle power supply system and from the battery at any given time. The device is furthermore designed to automatically provide the respective torque demand at any given time as a torque reference variable for controlling the electrical machine as a function of the respective requirements, at that time, for a positive or negative torque for the propulsion system, in which case changes in the voltage reference variable (U-LADE) downwards and upwards are limited by predetermined torque limit values for the electrical machine which define a torque tolerance band. Furthermore, changes in the torque reference variable upwards and downwards are limited by predetermined voltage limit values for the electrical machine, which form a voltage tolerance band. Means are provided for automatic cyclic checking of the reference variables. The electrical machine is controlled automatically by the voltage reference variable, but a change takes place to the torque reference variable for controlling the electrical machine, provided that the tolerance bands are complied with, when and for as long as the torque reference variable demanded from the electrical machine is a positive or negative torque, which is not the same as the predetermined torque on the electrical machine, in order to produce the charging voltage.
Accordingly, the stated object is achieved by a device and a method for operation of an electrical machine for a motor vehicle in accordance with the claims.
Advantages of the Invention
Both a boost function as well as a battery charging function and recuperation as well can always achieve their full effect in any vehicle situation and satisfy all the requirements of the “vehicle propulsion, battery and vehicle power supply” systems, provided that this is physically possible.
This avoids the time-consuming application (adaptation control device), which is susceptible to faults, of vehicle power supply system requirements and battery requirements for the propulsion system control, in particular for the internal combustion engine control device. The expression “recuperation” in this case means braking of the motor vehicle by means of the electrical machine by operating it in a predetermined manner as a generator.
Coordination of the braking torques and propulsion torques is possible only by taking into account “available torques” according to the invention. In addition to other advantages, this also makes it possible to compensate for recuperation torques by using a braking controller which can control the vehicle wheel axles individually.
The initial calculation of torques will be described in the following text, A function is provided by which missing input signals can be calculated in advance from output signals from the electrical machine, for example a generator. Among other variables, torque variables, for example, are calculated in advance for the unit coordinator (initial torque calculation). The function cycle time may, for example, be 50 ms or some other variable. Provision is preferably made for the instantaneous value of the generator current of the electrical machine to be determined from a family of characteristics via the rotation speed and the field current of the generator. A stored generator identification can be used to identify which generator is being used and which generator family of characteristics should be used. If the instantaneous voltage is not the same as the voltage in the family of characteristics, the generator current is corrected accordingly. If the electrical machine is in the full excitation range, then a correction current is determined from a family of characteristics via the rotation speed and the voltage, and is calculated using the generator current. Furthermore, the instantaneous value of the generator efficiency can be determined from a family of characteristics via the rotation speed and the power of the generator. The generator identification data is used to identify what generator is fitted in the motor vehicle and which family of characteristics should be used. The instantaneous value of the generator torque is calculated from the instantaneous values of the current, voltage, efficiency and rotation speed.
Generator charging torque (the torque which the electrical machine requires to charge the battery in the generator mode): the instantaneous value of the generator charging torque is calculated from the following vehicle power supply system variables: charging voltage, charging current, generator efficiency and generator rotation speed. If the device is in the charging mode, the process switches to the instantaneous value of the generator torque.
Minimum statistically possible generator charging torque (maximum statistically possible negative torque on the electrical machine in the generator mode): the maximum amount of power which can be drawn from the vehicle power supply system including its battery can be calculated from the following vehicle power supply system variables: recuperation voltage and recuperation current. The maximum power of the generator can be determined from a characteristic via the rotation speed of the electrical machine. The generator identification data can be used to identify what generator is installed in the motor vehicle, and which characteristic should be used. The lesser of these two variables is used, and this represents the narrower limit for the system. The maximum possible torque from this electrical machine at any given time when being operated as a generator can be calculated from this variable with the aid of the instantaneous efficiency and the rotation speed of this electrical machine.
Maximum statistically possible generator charging torque (the minimum statistically possible torque of the electrical machine as a generator and the maximum motor torque as a motor): the maximum power emitted from the vehicle power supply system including its battery can be calculated from the following vehicle power supply system variables: minimum voltage and maximum current. The minimum motoring power of the electrical machine when operating as a generator can be determined from an applicable fixed value using the generator rotation speed. For this purpose, it is possible to identify from the generator identification what electrical machine is installed as a generator, and which fixed value should be used. The larger of these two variables is used, and this represents the narrower limit for the system. The minimum possible torque for the electrical machine at any given time when being operated as a generator and the maximum possible torque for the electrical machine when being operated as a motor can be calculated from this variable with the aid of the instantaneous efficiency and the rotation speed of the electrical machine.
The minimum dynamically possible generator charging torque for the electrical machine is equal to the minimum static generator charging torque when the battery is empty and the recuperation voltage U-Rekup is equal to the maximum voltage U-Grenz.
The stated determination processes and calculations can each be carried out automatically by control devices.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.